In a printing machine, for example, in an electrophotographic printing machine, toner is transferred onto a printable material by an inking device. To fuse the toner to the printable material the toner is liquefied by the application of heat simultaneously with the pressure, so that it flows into the printable material and becomes intermeshed therein.
For the simultaneous application of heat and pressure, the printable material is transported by conveyers to the nip area between a heatable fuser roller and a backing roller. The printable material is often in the form of sheets. These sheets are often made of paper that can be constituted such that assimilation of the toner is facilitated.
In a fuser mechanism of this type the fuser roller is heated and at the same time it and the inking roll are pressed against one another. For this operation the fuser roller can be installed to be stationary and the inking roll can be moveable in such a way that it is pressed against the fuser roller only for the period of time during which printable material is in the space between the fuser roller and the inking roll.
The fuser roller includes a hollow, cylindrically shaped metal body that can have a different coating depending upon the manufacturing process and its intended use. The coating should in any case be able to yield at least to some degree to the pressure of the inking roll. This will assure that the toner remains for a longer period of time within the nip area between the inking roll and the fuser roller.
In most cases the fuser roller is heated from the inside outwards. The heat source in such cases is usually an infrared radiator. A heat source is located inside the fuser roller. It heats the cylinder shaped body of the fuser roller, preponderantly without touching. Flanges are located at the two ends of the body. The flange and the body are usually connected by a press fit or by welding, followed by reforming of the flange and the body. This results in rigid connections.
The body of the fuser roller and its coating are such that the best possible heat transfer from inside outwards is assured. Within the nip area between the fuser roller and the inking roll, the outer surface of the fuser roller reaches a temperature between 150° C. and 220° C. during operation. This temperature is sufficient (1) to melt the toner on the outer surface of the printable material and then (2) with the support of the pressure that is applied to work it into the printable material, where it later fuses following a cooling period.
When the fuser roller is heated, expansions occur that generate stresses on the connection points between the body and the flanges. The effects of these stresses can, e.g., be that the concentric operation of the fuser roller is adversely affected. Also, the connections between the body and the flanges are stressed so that their durability is reduced. The quality of the fusing characteristics of the entire fuser mechanism can be adversely affected by warping of the outer surface of the fuser roller.